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Modem
Registers
6.17
Programming
Suggestions and
Considerations
The
most
important
function of
a
modem
control
program
is
al-
ways
to
know
whether
the
modem
is
in
the
Command
or
On-line
State.
If
the
program
ever
gets
confused, data
passed
from
com-
puter
to
modem
may
be
construed
as a
command
and
vice
versa.
To
avoid the
consequences
that
could
result
from
this
confusion
please
make
note
of
the
following suggestions:
1.
Send
commands
to
the
modem
only
when
it
is
in
the
Com-
mand
State.
2.
Commands
entered
when
the
modem
is
in
the
On-line
State
are
considered data
and
will
be
output
as
such.
Be
sure to en-
ter
the
Escape
Code
before entering
commands.
3.
Data
output
by
the
computer
when
the
modem
is
in
the
On-
line
State
is
interpreted
as data.
Be
sure
to
enter
AT
O <CR>
to
re-enter the On-line
State after a
temporary
exit
to
the
Command
state.
4.
Do
not
have
the
computer echo
command
results
(either
word
or
number)
to
the
modem.
This
would
qualify as
random
data.
6.18
Command
Executions
Some commands
execute
in as
little
as
250
milliseconds (the Dial-
ing
command
being a notable exception).
For
the
computer
to
"catch" the
result
code,
be
sure
it is
prepared
to
do
so
within
this
time
constraint.
6-15
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